1. Field of the Invention
The present invention relates to a lateral position detecting apparatus for detecting the lateral position of a moving body such as a running vehicle.
2. Description of Related Art:
There is disclosed in U.S. Pat. No. 5,347,456 a conventional lateral position detecting apparatus. In this lateral position detecting apparatus, a magnetic field receiving device mounted on a vehicle is used for determining the lateral position of the vehicle running on a road by detection of a magnetic field generated by a plurality of markers installed on the surface of the road along the lateral center line of the road at certain intervals in the longitudinal direction.
In the conventional apparatus, however, the magnetic receiving device may receive the magnetic field generated by magnetized iron and steel bars used in a bridge or generated by the geomagnetism of the earth by mistake as if the magnetic field were generated by the markers. As a result, the conventional lateral position detecting apparatus has a problem that the accuracy of detection of the lateral position of the vehicle is deteriorated.
Specifically, since the markers are each also made of a permanent magnet, the markers generate a static magnetic field similar to that generated by magnetized iron and steel bars of the bridge or generated by the geomagnetism of the earth, making it impossible for the magnetic field receiving device to distinguish those from each other. As a result, it is obvious that the accuracy of detection of the lateral position of the vehicle is running is deteriorated.
This may be solved by employing magnetic field transmitting devices each for generating an alternating current magnetic field as markers. However, as the alternating current magnetic field varies alternately, an electromagnetic induction effect which is not observed in the case of a static magnetic field is induced.